Spin and Hyperfine Structure of Arsenic-76

Hyperfine structure in the ⁴S3/2 ground state of the radioactive atom As⁷⁶ has been investigated by the method of magnetic resonance in an atomic beam produced by microwave discharge dissociation of arsenic vapor. ΔF=0 resonances were observed within both the F=5/2 and F=7/2 atomic levels at several values of magnetic field up to about 5 oe, indicating that the spin of the As⁷⁶ nucleus is 2. An analysis of multiple quantum transition spectra within the same F states gave a measurement for two of the hfs intervals: Δν7/2,5/2=±(117±4) Mc/sec and Δν5/2,3/2=±(69±16) Mc/sec, with the same sign for both. From the value of the hfs constant A, the magnitude of the magnetic field at the arsenic nucleus is (1.33±{}0.15)×{}10⁵ oe in reasonable agreement with the variation in this field among similar atoms. The value of gJ has been found to be 1.994±{}0.003 for arsenic.